late 14c., from Old French transposer "transfer, remove; present, render symbolically" (14c.), from Latin transponere (past participle transpositus) "to place over, set over," from trans- "over" (see trans-) + ponere "to put, place" (past participle positus; see position (n.)). Form altered in French on model of poser "to put, place." Sense of "put music in a different key" is from c. 1600. Related: Transposed; transposing.